Role of Translesion Synthesis DNA Polymerases in DNA Replication in the Presence of a Weak DNA Polymerase {delta} in Saccharomyces cerevisiae

Translesion synthesis (TLS) DNA polymerases (pols) are often mutagenic for lesion bypass due to their low fidelity. Here, we isolated a weak yeast DNA pol mutant that possessed amino acid substitution V592G by genetic selection. The pol3-V592G cells were sensitive to hydroxyurea (HU), which increases the requirement for dNTPs, and their HU sensitivity was suppressed by L612M substitution. We also demonstrated that V592G substitution suppressed the phosphonoacetic acid (PAA) sensitivity of pol3-L612M cells, suggesting a cycle of mutual suppression in the HU- and PAA-sensitive yeast DNA pol mutants as similarly observed in the optA1- and PAA-sensitive T4 DNA pol mutants. However, the HU-sensitive pol3-V592G cells exhibited a mutator phenotype, which is contrast to the optA1-senisitive T4 phages that have an antimutator phenotype. Analysis of mutation spectra demonstrated that DNA pol participated in DNA replication in pol3-V592G cells in the presence of MMR, which extends earlier findings indicating that DNA pol contributes to DNA replication by a weak DNA pol . Importantly, we determined the true replication fidelity of pol3-V592G cells in the absence of MMR for the first time since replication errors could be masked by MMR, and thus demonstrated that DNA pol or a combination of DNA pols and contributed to replication errors in pol3-V592G cells. Overall, our observations suggest that the decreased polymerase activity of pol3-V592G cells resulted in increased TLS and reduced homologous recombination (HR).

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